The present embodiments relate to selecting at least one measurement field of a measurement chamber for dose monitoring when making an x-ray recording of an object.
In x-ray technology, a situation that regularly arises is that a utilized amount of radiation or x-ray dose in the case of x-ray examinations is to stay within a desired value range in order to provide a high image quality of the x-ray image. In the case of a dose that is too low, underexposed x-ray recordings are obtained, while a dose that is too high would lead to overexposure. If the dose lies outside of the work range, either the amount of light or energy generated at the outlet is too low, and the images obtained do not have a sufficiently high quality for medical diagnostics, or else the amount of dose is too high. In the case of a dose that is too high, changes in the dose, caused by differing absorption of the tissue of the radiation patient, are no longer converted into a proportional change in the light or energy signal. The generated images then likewise may not be used for medical diagnostics due to the lack of contrast.
It is for this reason that an automatic exposure control (AEC) may be used in x-ray technology. AEC is described, for example, in the document 2007/0025525 A1. Such an automatic exposure control or such an AEC system may be connected to every modern generator and is already available in many devices. Measurement detectors in the region of the image receiver surface provide the x-ray generator with a switch-off signal after reaching the required dose. By way of example, ionization chambers, photomultipliers or semiconductor radiation receivers are used as measurement detectors. The measurement detectors may be arranged in a measurement chamber and form measurement fields in the measurement chamber. Previously, work was generally undertaken with measurement chambers that have three measurement fields (e.g., a three-chamber system).
The arrangement of these three measurement fields in a three-chamber system is shown in, for example, FIG. 2 of the present application or in FIGS. 1a and 1b of US 2007/0025525 A1. When examining a patient, the measurement chamber is aligned with the organ or body part to be examined. Specific measurement fields for the automatic exposure control are then used depending on organ or body part. There are specific stipulations for the medical practitioner as to which measurement fields are to be used for which examination. By way of example, if the head is examined, only the central measurement chamber I from FIG. 2 may be used, while all three measurement chambers are used in, for example, a pelvic examination. Therefore, there is a relatively fixed predetermined relationship in the medical literature between the organ or body part and the measurement chamber or chambers of a three chamber measurement system to be used. This is used in organ programs, in which there may be an automatic selection of measurement chambers.
In a recent development, measurement chambers with a larger number of measurement fields are used. One new system is the five-chamber system. By way of example, such a system is shown in FIG. 4. A five-chamber system or a five-field measurement chamber has a symmetric design. In this chamber, at most three fields are used (e.g., the assignment of organ or body part to employed chamber, as is conventional in medicine, continues to be used in principle). An advantage of the five-field measurement chamber is that if the orientation of the patient is changed, this is not accompanied by a change in the orientation of the measurement chamber, but rather, the correct orientation of the measurement chamber is provided by selecting the at most three measurement fields to be used. By way of example, if the measurement chamber in FIG. 2 is provided for vertical orientation of the patient, the measurement chamber would be co-rotated in the case of rotation of the patient in the horizontal direction. This is not provided for in many systems, and x-ray recordings may thus only be made for one orientation of the patient.
These restrictions do not apply to the five-field measurement chamber from FIG. 4. By way of example, the measurement fields I, II and III may be used in the case of a vertical orientation of the patient, while use would be made of the measurement chamber triplet I, III and V or I, II and IV in the case of a vertical orientation. Therefore, there is no longer any need to rotate the measurement chamber, or x-ray recordings for different patient orientations become possible.
However, the use of measurement chambers with more than three fields (e.g., the use of five-field measurement chambers) also harbors difficulties. As a result of the larger number of possibilities, there is an increased risk of the incorrect measurement chambers being selected. In general, an incorrect selection leads to an incorrect exposure. As a result of this, the generated images become useless. Therefore, attempts have been made to provide a safer operation. Thus, it has been proposed to project (e.g., by light) the position of the selected measurement fields (e.g., the contours thereof) onto the patient in order thus to supply the user with feedback about the correctness of the selected chambers. By way of example, such systems are described in US 2007/0025525 A1 and in WO 2007/148262 A1. By way of example, the publication “Optimale Patientenpositionierungen in der Radiographie durch Videounterstützung [Ideal patient positioning in radiography by means of video assistance]” (see http://ip.com/IPCOM/000207924) also describes a camera system that establishes the location of the patient relative to the measurement fields of an AEC chamber from the image of the camera with the aid of pattern recognition algorithms.